Field of the Invention
The present invention relates to wireless communication and, more particularly, to a method and apparatus for performing hybrid automatic repeat request (HARQ) in a carrier aggregation system.
Related Art
Carrier aggregation systems are getting attention these days. A carrier aggregation system refers to a broadband wireless communication system comprising more than one component carrier (CC) which provides bandwidth smaller than the target bandwidth of the broadband wireless communication system. In a carrier aggregation system, a term of a serving cell may be used instead of the term of a component carrier. A serving cell associated with the carrier aggregation system may consist of a pair of two component carriers such as a downlink component carrier (DL CC) and a uplink component carrier (UL CC) or consist only of DL CCs. A carrier aggregation system is such a kind of system where a plurality of serving cells is associated with one user equipment.
Conventional carrier aggregation systems allowed aggregating only those component carriers operating in the same scheme. In other words, the a priori art allowed aggregating only the component carriers operating based on the frequency division duplex (FDD) scheme or the time division duplex (TDD) scheme. In particular, in the case of TDD, it is assumed that component carriers to be aggregated are set up with the same uplink-downlink configuration (UL-DL configuration). UL-DL configuration is intended to inform in which subframe each individual subframe within a frame consisting of a plurality of subframes is used between a uplink (UL) subframe and a downlink (DL) subframe.
However, there are chances that future wireless communication systems may not be constrained to aggregate only those component carriers employing the same scheme. For example, component carriers operating based on the FDD scheme or component carriers consisting only of uplink subframes may be aggregated with component carriers operating based on the TDD scheme. Similarly, component carriers operating based on the TDD scheme may be aggregated with component carriers operating based on the FDD scheme. Or component carriers consisting only of uplink subframes may be aggregated with component carriers operating based on the TDD or FDD scheme.
As described above, in a carrier aggregation system where component carriers operating according to the schemes different from each other, it can be difficult or inefficient to directly apply a method for performing hybrid automatic repeat request (HARQ) which assumes aggregation of component carriers operating in the same scheme.
In a component carrier system aggregating component carriers operating according to different schemes from each other, there need a method and an apparatus for efficiently organizing a timing between scheduling information and scheduled data, a timing between the data and acknowledgement/not-acknowledgement (ACK/NACK) which is a response to the data, a timing between the ACK/NACK and data retransmission according to the ACK/NACK, and the like.